The pump has started to cycle for a fraction of a second every twenty servings or so. Just one quick movement of the pump. No leaks visible. Could it be the start of a failing pressure sensor in the pump? Assume I would have to replace the whole thing.

Ed, I was lucky enough to find a spare online for about $20 last year, but these pumps seem to generally run around $300. Having been doing research when I found it I found that there's reasonable access to parts including the bladders, etc. Mine had a broken pressure switch which I did find.

The pump is pretty simple overall, you may want to pull and see where the water's coming from and then find the replacement parts.

Jabsco has rebuild kits available for most pumps, so I would go that route. I carry a spare pump + a rebuild kit, so I tend to go the belt and suspenders route, which is a reasonable route given where BlueJacket lives.